Anode assembly for primary galvanic cell



lune 30, `1953 E. A. scHuMAcHER ETAL 2,64%024 ANODE ASSEMBLY FOR PRIMARY GALVNIC CELL Filed Sept. 28. 1949 INVENTORS n ERWIN A. SCHUMACHER GEORGE W. HEISE I l YAY lrlcl 'An All. It.. lufl underside Plaied Patented June 30, 1953 ANODE ASSEMBLY FOR PRIMARY l GALVANIC CELL Erwin A. Schumacher, Parma, and George W.

Heise, Cleveland, Ohio, assignors, by mesne assignments, to Union Carbide and Carbon Corporation, a corporation of New York Application September 28, 1949, Serial No. 118,206

Y. 4 Claims. l

This invention relates to primary galvanic cells and refers more particularly lto an anode assembly for primary galvanic cells of the type having an immobilized alkaline electrolyte.

In primary galvanic cells of the type utilizing a zinc electrode it is conventional practicev to amalgamate the zinc electrode to minimize localized corrosion and the formation of gas internally of the cell.

The use of amalgamated zinc as anodes in primary cells of the type employing an immobilizedalkaline electrolyte gives rise to special problems. In cells of this type the amalgamated anode must not emerge from the electrolyte because of excessive corrosionrof the zinc atthe air-electrolyte interface. Consequently, a metal connecting member must be attached to the anode and to an external terminal for the cell. The connector introduces new diiiiculties in that steel, which would otherwise be satisfactory for use as a connector is sufficiently cathodic to zinc to cause excessive corrosion of the zinc at the point of attachment of the connector to the anode leading to failure of the connection and consequent uselessness of the cell.

Proposals to overcome the diiiiculties caused by potential diierences between the metal of the connector and the zinc anode by employing for the connector a readily amalgamable metal such as copper or by copper-plating a steel or iron o connector have not satisfactorily solved the problem and actually have introduced a new problem. Thus, when the connector is amalgamable, mercury, released by electrochemical dissolution of the anode upon cell discharge, migrates along the connector past the sealing materials customarily used at the closure of the cell ultimately covering the external terminal surface. Protective coatings applied to the portions of the connector in the air space with which such cells are provided are lifted by the migrating mercury, permitting access of air to the anode and accelerated wasteful corrosion of the zinc.

The net result of such mercury creepage is a loss in cell effectiveness and a hazardfor the user of the cell. Mercury creepage destroysv sealing effectiveness and quite commonly is accompanied by leakage of electrolyte. Furthermore, in cells intended for intimate personal use, as 1n hearing aids, a freely exposed mercury surface is highly undesirable.

It is the principal object of this invention to solve these problems. More specically, it is an object of the invention to provide an anode assembly for use in a primary galvanic cell of the (Cl. 13G-135) 2 .1 type utilizing an immobilized alkaline, which assembly prevents migration of mercury externally of the cell. x

In accordance with the invention these objects are achieved by the interposition in an anode assembly of a barrier over which mercury can not readily pass. The invention comprises vthe combination of an amalgamated zinc electrode immersed in immobilized alkaline electrolyte and a metal connecting member emergent from the electrolyte and attached to the zinc electrode and to a metal member which serves bothas a closure and an external terminal for the cell,at leasta portion of at least one of such members having a difficultly-amalgamable surface. .I f

In the accompanying drawing:

Fig. l is a vertical sectional View of a primary galvanic cell having an immobilized alkaline electrolyte and provided'with an anode assembly according to the invention; and

Fig. 2 is a view of a modied form of anode assembly, part being broken away. Y

Referring to the drawing, there is shown in Fig. l a5 an example of the type of cell for which the invention is ideally suited, a cell of the type described in U. S. patent application Serial No. 52,018, filed September 30, 1948, by P.A. Marsal and R. P. Fox, nowPatent No. 2,597,116. This cell rcomprises a container I0 having apertures II, I2 for the admission of air to a -pair of airdepolarizable carbonaceous electrodes I3, I4. An immobilized aqueous `alkaline electrolyte I5 supported by a plurality of layers I6 of fibrous material occupies the space between thev electrodes I3, I4 and an amalgamated zinc electrode I'I, an air space IB being provided at one end of the cell. A connector member It is 'attached (suitably by'rivetting or welding) to -the' zinc electrodeli and to a metal closure member 20 which serves as an external terminal. AThe cell is sealed internally by a layer 2I of a suitable material such as wax.

In accordance with the invention the connector member I9 between the'amalgamated zinc electrode I'I and the closure-terminal :member 20 may be made of steel (or iron) or magnesium. When these members are made lof steel,itC is necessary that at least the portions of the connector member which are immersed in or wet by the electrolyte be coated with a readily-amalgamable metal such as copper (or brass), tin, or zinc to prevent setting up an iron-zinc couple. However, surfaces of either the closure-terminal member or the connector member or both which are not wet by electrolyte are not coated but present a bare iron surface which, being diilicultly amalgamable, provide a barrier over which mercury can not readily pass. In the modification shown in Fig. 1, the entire connector member I9 is coated, Ipreferably with copper, but the inner surface of the closure-terminal member `20 is uncoated. In the modication shown in Fig. '2, the lower portion of the connector member I9 is uncoated as is the inner surface of the closure` ,lO

terminal member 20. i

When the anode assembly of the invention including plated steel members as shown in Figs. 1-7 1 and 2 and as just described is inserted in the immobilized alkaline electrolyte of a primary cell,

the surf-aces which are plated .with readily-amalgamable metal are quickly amalgamated by Inercury migrating from the amalgamated anode. A The high hydrogen overvoltage of the amalgam` ated surface polarizes the zinc-connector cuany portion thereof be coated with readily-amalgamable metal. This is true because magnesium does not set up a potential difference with zinc in alkaline solution and there is therefore no danger of excessive, localized corrosion of zinc at the point of connection between the anode and the connector member. .Since magnesium is not amalgamated in contact with mercury, the connector member and -closure-terminal member when made of magnesium provideanefective barrier against mercury ,creepage The yconstruction of the anode assemblyof the invention when magnesium connector and closure-terminal members are employed is identical with that shown in the drawing save for. the elimination of the coating of amalgamable metal.

As indicated in the drawing, the external surfaces of the closure-terminal member of the anode assembly of the invention may be plated, if desired, suitably with brass, to present an attractive appearance and, particularly when the member is made of steel, to prevent interference with good electrical contact by the formationof rust.

Although the invention has been described with particular reference to one specific type of cell it is not limited to use in that cell but is applic-v able to any cell employing anramalgamated zinc electrode immersed in immobilized alkaline electrolyte.

As used lherein, the term steeP includes any steel or iron-base alloy the surface of which is not amalgamable in contact with mercury ,and alkaline electrolyte, and the term magnesium includes anymagnesium base alloy whichy is not amalgamable under the same conditions.

We claim:

1. An air-depolarized primary galvanic cell Y electrolyte;

comprising in combination a container closed at one end only and having an aperture in its side walls for entry of air; an air-depolarizable carbonaceous electrode covering said aperture; terminal means extending through said closed end of saidcontainerand making electrical contact with saidcarbonaceous electrode.; an immobilized electrolyte; an amalgamated zinc electrode in said a unitary metal closure-terminal member forming a seal in cooperation with said side-walls for the open end of said container; and a'metal connecting member having one of its ends attached .to said closure-terminal member outsidefof. said electrolyte and its other end immersed in said electrolyte and electrically connected to said amalgamated zinc electrode, at least a portion of at least one of said members having a difcultly amalgamable surface extending across the possible path of mercury migration, thereby preventing migration of mercury from said zinc electrode, consequent disruption of said seal, and eventual escape of mercury from the cell.

2. An air-depolarized primary galvanc cell comprising in combination a container closed at one end only and having an aperture in its side Walls for entry of air; an air-depolarizable carbonaceous electrode covering said aperture; terminal means extending through said closed end of said container and making electrical contact with said carbonaceous electrode; an immobilized electrolyte; an amalgamated zinc electrode in said electrolyte; a unitary metal closure-terminal member forming a seal in cooperation with said sidewalls for the open end of said container; and a metal connecting member having one of its ends attached to said closure-terminal member@ outside of said electrolyte and its other end immersed in said electrolyte and electrically connected to said amalgama-ted zinc electrode, at leastthe portion of said connecting member attached to said zinc electrode having a readilyamalgamablev surface and at least a portion of said terminal-closurefmember having a diicultly amalgamable surface extending across the possible path-of mercury migration, thereby preventing migrationof mercury from said zinc electrode, consequent disruption of said seal, and eventual escape of mercury from the cell.

3. In the combination defined by claim 1, a magnesium connecting member and a magnesium closure-terminal member.

4. In thecombination dened by claim 2, a steel connecting member and a steel closure-terminal member at least the portion of said connecting member attached to said zinc electrode being copper coated. i ERWIN A.v SCHUMACHER.

GEORGEVW. HEISE.

Number Name Date 425,818 McLaughlin Apr. 15, 1890 27,491,879 Teague Dec. 20, 1949 

1. AN AIR-DEPOLARIZED PRIMARY GALVANIC CELL COMPRISING IN COMBINATION A CONTAINER CLOSED AT ONE END ONLY AND HAVING AN APERTURE IN ITS SIDE WALLS FOR ENTRY OF AIR-DEPOLARIZABLE CARBONACEOUS ELECTRODE COVERING SAID APERTURE; TERMINAL MEANS EXTENDING THROUGH SAID CLOSED END OF SAID CONTAINER AND MAKING ELECTRICAL CONTACT WITH SAID CARBONACEOUS ELECTRODE; AN IMMOBILIZED ELECTROLYTE; AN AMALGAMATED ZINC ELECTRODE IN SAID ELECTROLYTE; A UNITARY METAL CLOSURE-TERMINAL MEMBER FORMING A SEAL IN COOPERATION WITH SAID SIDE-WALLS FOR THE OPEN END OF SAID CONTAINER; AND A METAL CONNECTING MEMBER HAVING ONE OF ITS ENDS ATTACHED TO SAID CLOSURE-TERMINAL MEMBER OUTSIDE OF SAID ELECTROLYTE AND ITS OTHER END IMMERSED IN SAID ELECTROLYTE AND ELECTRICALLY CONNECTED TO SAID AMALGAMATED ZINC ELECTRODE, AT LEAST A PORTION OF AT LEAST ONE OF SAID MEMBERS HAVING A DIFFICULTY AMALGAMABLE SURFACE EXTENDING ACROSS THE POSSIBLE PATH OF MERCURY MIGRATION, THEREBY PREVENTING MIGRATION OF MERCURY FROM SAID ZINC ELECTRODE, CONSEQUENT DISRUPTION OF SAID SEAL, AND EVENTUAL ESCAPE OF MERCURY FROM THE CELL. 